1,845 research outputs found
The model of dynamo with small number of modes and magnetic activity of T Tauri stars
The model that describes operation of dynamo in fully convective stars is
presented. It is based on representation of stellar magnetic field as a
superposition of finite number of poloidal and toroidal free damping modes. In
the frame of adopted low of stellar differential rotation we estimated minimal
value of dynamo number D, starting from which generation of cyclic magnetic
field in stars without radiative core is possible. We also derived expression
for period of the cycle. It was found that dynamo cycles of fully convective
stars and stars with thin convective envelopes differ in a qualitative way: 1)
distribution of spots over latitude during the cycle is different in these
stars; 2) the model predicts that spot formation in fully convective stars
should be strongly suppressed at some phases of the cycle.
We have analyzed historical lightcurve of WTTS star V410 Tau and found that
long term activity of the star is not periodic process. Rather one can speak
about quasi cyclic activity with characteristic time of yr and chaotic
component over imposed. We concluded also that redistribution of cool spots
over longitude is the reason of long term variations of V410 Tau brightness. It
means that one can not compare directly results of photometric observations
with predictions of our axially symmetric (for simplicity) model which allows
to investigate time evolution of spot's distribution over latitude. We then
discuss what kind of observations and in which way could be used to check
predictions of the dynamo theory.Comment: 18 pages, 5 figures, accepted to Astron. Let
Abnormal phenomena in a one-dimensional periodic structure containing left-handed materials
The explicit dispersion equation for a one-dimensional periodic structure
with alternative layers of left-handed material (LHM) and right-handed material
(RHM) is given and analyzed. Some abnormal phenomena such as spurious modes
with complex frequencies, discrete modes and photon tunnelling modes are
observed in the band structure. The existence of spurious modes with complex
frequencies is a common problem in the calculation of the band structure for
such a photonic crystal. Physical explanation and significance are given for
the discrete modes (with real values of wave number) and photon tunnelling
propagation modes (with imaginary wave numbers in a limited region).Comment: 10 pages, 4 figure
A pair of gametologous genes provides further insights into avian comparative cytogenomics
Exploration of avian gametologous genes, i.e., homologous genes located on both the Z and W chromosomes, provides a crucial information about the underlying mechanism pertaining to the evolution of these chromosomes. The domestic chicken (Gallus gallus (Linnaeus 1758); GGA) traditionally serves as the primary reference subject of these comparative cytogenomic studies. Using bioinformatic, molecular (overgo BAC library scanning), and cytogenetic (BAC-based FISH) techniques, we have investigated in detail a pair of UBE2R2/UBE2R2L gametologs. By screening a gridded genomic jungle fowl BAC library, CHORI-261, with a short labeled UBE2R2L gene fragment called overgo probe, we detected seven specific clones. For three of them, CH261-019I23, CH261-105E16, and CH261-114G22, we identified their precise cytogenetic location on the Gallus gallus W chromosome (GGAW). They also co-localized with the UBAP2L2 gene on the, as was shown previously, along with the CH261-053P09 BAC clone also containing the GGAW-specific UBE2R2L DNA sequence. The fine mapping of the UBE2R2/UBE2R2L homologs in the chicken genome also shed the light on comparative cytogenetic aspects in birds. Our findings provided further evidence that bird genomes moderately changed only during evolution and are suitable for successful use of interspecies hybridization using both overgo-based BAC library screen and BAC-based FISH
Correction to: A pair of gametologous genes provides further insights into avian comparative cytogenomics
Biologia
https://doi.org/10.1007/s11756-023-01395-6
The original article has been updated to reflect added changes in the list of references. The original article has been corrected
Optical gain in one-dimensional photonic band gap structures with n-i-p-i crystal layers, Journal of Telecommunications and Information Technology, 2002, nr 1
The gain enhancement in a layered periodic photonic band gap structure containing active medium based on GaAs n-i-p-i superlattices separated by AlGaAs layers is analyzed. The dependences of extinction coefficient and refractive index on excitation level and wavelength are presented. Transmission characteristics of a probe light versus excitation level are calculated. It is shown that the threshold of generation can be essentially reduced if the wavelength of probe light falls to the band gap edge
Intrinsic room temperature ferromagnetism in Co-implanted ZnO
We report on the structural and magnetic properties of a cobalt-implanted ZnO film grown on a sapphire substrate. X-ray diffraction and transmission electron microscopy reveal the presence of a ( )-oriented hexagonal Co phase in the Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter of about 5-6 nm, form a Co rich layer in the substrate close to the ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two different magnetic phases in the implanted region. One originates from the Co clusters in Al2O 3, the other one belongs to a homogeneous ferromagnetic phase with a ferromagnetic Curie temperature far above room temperature. In the latter case, the ferromagnetism can be attributed to Co substitution on Zn sites in the ZnO layer. We have observed magnetic dichroism at the Co L2,3 and O K edges at room temperature as well as the multiplet structure in x-ray absorption spectra around the Co L3 edge, supporting the intrinsic nature of the observed ferromagnetism in a Co-implanted ZnO film. The magnetic moment per substituted cobalt is found to be about 2.81 Ξ½B, which is very close to the theoretical expected value of 3 Ξ½B/Co for Co 2+ in its high spin state. Β© 2008 IOP Publishing Ltd
Interacting circular nanomagnets
Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in
diameter) were prepared by the method of the electron lithography. The
magnetization curves were studied by Hall magnetometry with the compensation
technique for different external field orientations at 4.2K and 77K. The shape
of hysteresis curves indicates that there is magnetostatic interaction between
the particles. The main peculiarity is the existence of remanent magnetization
perpendicular to easy plain. By numerical simulation it is shown, that the
character of the magnetization reversal is a result of the interplay of the
interparticle interaction and the magnetization distribution within the
particles (vortex or uniform).Comment: 16 pages, 8 figure
ΠΡΠΈΠΌΠΏΡΠΎΡΠΈΠΊΠ°, ΡΡΡΠΎΠΉΡΠΈΠ²ΠΎΡΡΡ ΠΈ ΠΎΠ±Π»Π°ΡΡΡ ΠΏΡΠΈΡΡΠΆΠ΅Π½ΠΈΡ ΠΏΠ΅ΡΠΈΠΎΠ΄ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ ΡΠΈΠ½Π³ΡΠ»ΡΡΠ½ΠΎ Π²ΠΎΠ·ΠΌΡΡΡΠ½Π½ΠΎΠΉ ΠΏΠ°ΡΠ°Π±ΠΎΠ»ΠΈΡΠ΅ΡΠΊΠΎΠΉ Π·Π°Π΄Π°ΡΠΈ Ρ Π΄Π²ΡΠΊΡΠ°ΡΠ½ΡΠΌ ΠΊΠΎΡΠ½Π΅ΠΌ Π²ΡΡΠΎΠΆΠ΄Π΅Π½Π½ΠΎΠ³ΠΎ ΡΡΠ°Π²Π½Π΅Π½ΠΈΡ
For a singularly perturbed parabolic problem with Dirichlet conditions we prove theΒ existence of a solution periodic in time and with boundary layers at both ends of the space interval inΒ the case that the degenerate equation has a double root. We construct the corresponding asymptoticΒ expansion in a small parameter. It turns out that the algorithm of the construction of the boundaryΒ layer functions and the behavior of the solution in the boundary layers essentially diο¬er from that onesΒ in case of a simple root. We also investigate the stability of this solution and the corresponding regionΒ of attraction.ΠΠ»Ρ ΡΠΈΠ½Π³ΡΠ»ΡΡΠ½ΠΎ Π²ΠΎΠ·ΠΌΡΡΡΠ½Π½ΠΎΠΉ ΠΏΠ°ΡΠ°Π±ΠΎΠ»ΠΈΡΠ΅ΡΠΊΠΎΠΉ Π·Π°Π΄Π°ΡΠΈ Ρ ΠΊΡΠ°Π΅Π²ΡΠΌΠΈ ΡΡΠ»ΠΎΠ²ΠΈΡΠΌΠΈΒ ΠΠΈΡΠΈΡ
Π»Π΅ ΠΏΠΎΡΡΡΠΎΠ΅Π½ΠΎ ΠΈ ΠΎΠ±ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΎ Π°ΡΠΈΠΌΠΏΡΠΎΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ ΡΠ°Π·Π»ΠΎΠΆΠ΅Π½ΠΈΠ΅ ΠΏΠ΅ΡΠΈΠΎΠ΄ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΏΠΎ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ ΡΠ΅ΡΠ΅Π½ΠΈΡ Ρ ΠΏΠΎΠ³ΡΠ°Π½ΠΈΡΠ½ΡΠΌΠΈ ΡΠ»ΠΎΡΠΌΠΈ Π²Π±Π»ΠΈΠ·ΠΈ ΠΊΠΎΠ½ΡΠΎΠ² ΠΎΡΡΠ΅Π·ΠΊΠ° Π² ΡΠ»ΡΡΠ°Π΅, ΠΊΠΎΠ³Π΄Π° Π²ΡΡΠΎΠΆΠ΄Π΅Π½Π½ΠΎΠ΅ ΡΡΠ°Π²Π½Π΅Π½ΠΈΠ΅Β ΠΈΠΌΠ΅Π΅Ρ Π΄Π²ΡΠΊΡΠ°ΡΠ½ΡΠΉ ΠΊΠΎΡΠ΅Π½Ρ. ΠΠΎΠ²Π΅Π΄Π΅Π½ΠΈΠ΅ ΡΠ΅ΡΠ΅Π½ΠΈΡ Π² ΠΏΠΎΠ³ΡΠ°Π½ΠΈΡΠ½ΡΡ
ΡΠ»ΠΎΡΡ
ΠΈ ΡΠ°ΠΌ Π°Π»Π³ΠΎΡΠΈΡΠΌ ΠΏΠΎΡΡΡΠΎΠ΅Π½ΠΈΡΒ Π°ΡΠΈΠΌΠΏΡΠΎΡΠΈΠΊΠΈ ΡΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎ ΠΎΡΠ»ΠΈΡΠ°ΡΡΡΡ ΠΎΡ ΡΠ»ΡΡΠ°Ρ ΠΎΠ΄Π½ΠΎΠΊΡΠ°ΡΠ½ΠΎΠ³ΠΎ ΠΊΠΎΡΠ½Ρ Π²ΡΡΠΎΠΆΠ΄Π΅Π½Π½ΠΎΠ³ΠΎ ΡΡΠ°Π²Π½Π΅Π½ΠΈΡ.Β ΠΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ ΡΠ°ΠΊΠΆΠ΅ Π²ΠΎΠΏΡΠΎΡ ΠΎΠ± ΡΡΡΠΎΠΉΡΠΈΠ²ΠΎΡΡΠΈ ΠΏΠ΅ΡΠΈΠΎΠ΄ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠ΅ΡΠ΅Π½ΠΈΡ ΠΈ ΠΎΠ±Π»Π°ΡΡΠΈ Π΅Π³ΠΎ ΠΏΡΠΈΡΡΠΆΠ΅Π½ΠΈΡ
High-temperature ferromagnetism in Co-implanted TiO2 rutile
We report on structural, magnetic and electronic properties of Co-implanted TiO2(1 0 0) rutile single crystals for different implantation doses. Strong ferromagnetism at room temperature and above is observed in TiO 2 rutile plates after cobalt ion implantation, with magnetic parameters depending on the cobalt implantation dose. While the structural data indicate the presence of metallic cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra provides evidence that a sizeable portion of the dopants occupy substitutional Co2+ sites. The detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the rutile phase, and the second one is a superparamagnetic phase which originates from the formation of metallic cobalt clusters in the implanted region. Using x-ray resonant magnetic scattering, the element specific magnetizations of cobalt, oxygen and titanium in Co-implanted TiO2 single crystals are investigated. Magnetic dichroism was observed at the Co L2,3 edges as well as at the O K edge. Anomalous Hall effect measurement indicates n-type carriers in Co-implanted TiO 2 rutile. The interaction mechanism, which leads to ferromagnetic ordering of substituted cobalt ions in the host matrix, is also discussed. Β© 2009 IOP Publishing Ltd
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